The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
A hybrid transmission combines and transfers torque from various torque actuators to a drivetrain to provide tractive force for a vehicle. Torque actuators may include internal combustion engines and non-combustion machines including e.g., electric motors, hydraulic motors, and mechanical motors. Non-combustion machines may be controlled to generate torque or generate storable energy. For example, an electric motor may generate electricity that is immediately used in another electric motor or is remotely stored in a battery or high-voltage capacitor.
Paired electric motors may include a first motor configured to generate torque and a second motor configured to generate electricity. However, both the first and second motors may be capable of generating torque and electricity as required. Thus, during ongoing operation, the second motor may operate in a torque-generative mode to provide supplemental torque to the first motor to provide additional tractive force when torque demands are high.
Hybrid transmissions may utilize a differential gear set and clutches to manage torque between the torque actuators and the drivetrain. Through various clutch actuations the hybrid transmission may operate in one of several fixed gear modes or in a variable gear ratio mode. The differential gear arrangements typically include a sun gear, planetary gears, and a ring gear that meshingly engage and interact to transfer torque.
Each meshed gear interaction includes lash, i.e., a clearance that occurs between mating components of the gears. Lash has no effect when the gears are transferring torque. Lash may manifest itself in audible noise, e.g., as a rattle or clunk when the clearance between mating components of the gears is taken up during a torque transition. Torque transitions include initiating torque transfer from rest, stopping torque transfer during a coastdown, or reversing direction of torque transfer. Excessive lash is known to affect gear durability and cause torque transfer delays as the clearance between the mating components of the gears is taken up during a torque transition.
Audible noise associated with lash during a torque transition may be noticeable and objectionable when an electric motor reverses torque direction. Such audible noise may be generated by engine torque that is transferred to a transmission during torque reversal in an electric motor coupled to the transmission.